1. Field of the Invention
The invention relates to an apparatus for increasing the efficiency of fractional distillation trays. The invention more specifically relates to a process and apparatus providing a higher efficiency multiple downcomer fractionation tray.
2. Related Art
Multiple downcomer fractionation trays were introduced by U.S. Pat. No. 3,410,540 issued to W. Bruckert. This reference describes the characteristic structure and arrangement of the components of a multiple downcomer tray. These include long, narrow, trough-like downcomers spread across the tray with long rectangular areas of tray decking separating the downcomers. The traditional rectangular shape of the downcomers and transverse arrangement of downcomers on vertically adjacent trays is also shown.
Multiple downcomer trays are noted for their high capacity. They were therefore included in an article entitled xe2x80x9cHigh-Capacity Distillationxe2x80x9d published at page 53 of the August 1998 edition of Hydrocarbon Processing and in an article starting at page 23 of the January 1999 edition of Chemical Engineering Process. These articles show the transverse arrangement of the downcomers on vertically adjacent trays and describe the flow of vapor and liquid through fractionation columns employing these trays.
Liquid which falls from the bottom of a downcomer of a multiple downcomer tray falls onto the active vapor-liquid contacting area of the next lower tray. It has been recognized in the art that the liquid falling on the decking could penetrate the decking, thus bypassing the intended vapor-liquid contacting. U.S. Pat. No. 5,209,875 introduced the use of antipenetration pans suspended between the decking and the downcomer to reconcile this problem. The antipenetration pans are located under the liquid outlets of the upper tray""s downcomer and oriented perpendicular to the downcomers of the lower tray. Liquid exiting the downcomers falls upon the pans and then flows onto the decking of the lower tray.
The invention is a novel apparatus designed to increase the efficiency of fractionation columns which contain multiple downcomer fractionation trays. The apparatus comprises a liquid distribution pan suspended between vertically adjacent trays which are mounted transverse to each other. The distribution pan collects liquid emanating from the downcomer of the upper tray and then discharges it in a desired pattern across the active decking area of the next lower tray. This causes the liquid to fall upon the lower tray at a set uniform distance from the inlet to the downcomer of the lower tray. All of the liquid then has a uniform residence time upon the tray, thus increasing the separation efficiency of the tray.
One broad embodiment of the invention may be characterized as a fractional distillation process which comprises passing a liquid comprising a first component and a second component onto an upper first tray located in a fractional distillation column containing a plurality of vertically spaced apart multiple downcomer fractionation trays and operated at fractionation conditions which causes vapor to rise through decking areas provided on the trays while liquid is simultaneously collected in at least one downcomer forming part of each tray, with liquid which has been collected in a downcomer of the first tray exiting the downcomer through openings located in a lower portion of the downcomer; collecting liquid, which is passing downward from said openings in the lower portion of the downcomer of the first tray, in a liquid collection and distribution pan suspended between the first tray and a lower, second tray; and discharging liquid from the liquid collection pan onto the decking area of the second tray in a pattern aligned parallel to a downcomer of the second tray.
A second broad embodiment of the invention is an apparatus for performing fractional distillation in a fractionation column, which apparatus comprises an upper first tray and a lower second tray, with both the first and second trays comprising a trough-shaped downcomer and vapor-liquid decking panels adjacent the downcomer, and with the downcomer of the first tray being oriented transverse to the downcomer of the second tray and having at least two groups of liquid outlets in the bottom of the downcomer; and a liquid distribution device mounted at an intermediate level between the downcomers of the first tray and the decking of the second tray, the liquid distribution device being of sufficient length to receive liquid falling from the liquid outlets of at least two downcomers of the first tray and having at least one row of liquid outlets aligned parallel with the downcomer of the second tray, whereby liquid from the first tray falling into the liquid distribution device is distributed across a decking panel of the lower second tray at a uniform distance from the downcomers adjacent to the decking panel.